Preliminary study on the dynamic mechanical thermal analysis of polymer foams for use in impact resistant systems design

The objective of this research was to assess the utility of dynamic mechanical thermal analysis (DMTA) in investigation of polymer-based foams for the potential use in anti-impact protection systems. Therefore, three different types of specimens were chosen (polyolefin, polyurethane, rubber) and examined with: i. amplitude (1-100 µm), ii. frequency (0.1-100 Hz), iii. temperature (-60-60°C) sweeps. These DMTA modes enabled to successfully mimic: i. deformation during the impact, ii. foam behaviour while worn (low frequencies) and hit (high frequencies), iii. summer and winter conditions. Among others, investigation of loss angle tangent (tanδ), being a ratio between loss (E'') and storage (E') moduli, favourably revealed an inverse relationship between the tanδ at 100 Hz and maximum impact force needed to destroy the specimen. It was also established that a compromise between elastic (E') and viscous (E'') needs to be maintained to preserve shape stability while dissipating energy to achieve the high compressive strength (CS), e.g., more viscous rubber foam - CS of approx. 86 kPa (tanδ = 0.44), rigid polyolefin foam - CS at the level of 36 kPa (tanδ = 0.15). Therefore, DMTA successfully served as a complementary tool, providing mechanistic insight that supported and explained trends observed in conventional compression and impact testing.